New Phases and Dissociation-Recombination of Hydrogen Deuteride to 3.4 Mbar

Dias, Ranga; Noked, Ori; Silvera, Isaac F.

doi:10.1103/physrevlett.116.145501

Cited by 25 publications

(24 citation statements)

References 42 publications

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“…This implies a non-centrosymmetric structure and a weakening of the molecules. In studies of HD a process of bond dissociation and recombination ("DISREC", 2HD → H 2 + D 2 ) has been observed 50 . This bond breaking is seen in DFT to also occur in pure H 2 26,30 .…”

Section: à ámentioning

confidence: 99%

Understanding high pressure molecular hydrogen with a hierarchical machine-learned potential

2020

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The hydrogen phase diagram has several unusual features which are well reproduced by density functional calculations. Unfortunately, these calculations do not provide good physical insights into why those features occur. Here, we present a fast interatomic potential, which reproduces the molecular hydrogen phases: orientationally disordered Phase I; broken-symmetry Phase II and reentrant melt curve. The H2 vibrational frequency drops at high pressure because of increased coupling between neighbouring molecules, not bond weakening. Liquid H2 is denser than coexisting close-packed solid at high pressure because the favored molecular orientation switches from quadrupole-energy-minimizing to steric-repulsion-minimizing. The latter allows molecules to get closer together, without the atoms getting closer, but cannot be achieved within in a close-packed layer due to frustration. A similar effect causes negative thermal expansion. At high pressure, rotation is hindered in Phase I, such that it cannot be regarded as a molecular rotor phase.

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Section: à ámentioning

confidence: 99%

Understanding high pressure molecular hydrogen with a hierarchical machine-learned potential

2020

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“…Rich physics and chemistry have been discovered, and are still being predicted in both pure hydrogen [1][2] [3] and hydrogen-rich compounds [4][5] [6] [7]. Dense solid hydrogen shows an unexpectedly complicated phase diagram [8][9][10] [11][12] [13][14] [15] with an anomalous melting curve maximum and minimum [3][16] [17][18] [19][20] [21], embodying solid states based around free rotating molecules (Phase I), broken symmetry due to quadrupole interactions (Phase II), packing of weakly bonded molecules (Phase III), and proposed "mixed" state (phases IV and V). The latter two phases have alternating layers of rotating molecules similar to Phase I, and weak molecules akin to Phase III [1] [13][14] [15].…”

Section: Introductionmentioning

confidence: 99%

Thermodynamic anomalies and three distinct liquid-liquid transitions in warm dense liquid hydrogen

Geng

Wu²,

Marqués

et al. 2019

Phys. Rev. B

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The properties of hydrogen at high pressure have wide implications in astrophysics and high-pressure physics. Its phase change in the liquid is variously described as a metallization, H2-dissociation, density discontinuity or plasma phase transition. It has been tacitly assumed that these phenomena coincide at a first-order liquid-liquid transition (LLT). In this work, the relevant pressure-temperature conditions are thoroughly explored with first-principles molecular dynamics. We show there is a large dependency on exchange-correlation functional and significant finite size effects. We use hysteresis in a number of measurable quantities to demonstrate a first-order transition up to a critical point, above which molecular and atomic liquids are indistinguishable. At higher temperature beyond the critical point, H2-dissociation becomes a smooth cross-over in the supercritical region that can be modelled by a pseudo-transition, where the H2→2H transformation is localized and does not cause a density discontinuity at metallization. Thermodynamic anomalies and counter-intuitive transport behavior of protons are also discovered even far beyond the critical point, making this dissociative transition highly relevant to the Supplementary Material. Results of dimer-dimer bond-length distribution (DDLD) calculations, comparison between PBE and vdW-DF results, the thermodynamic modelling of pseudo-transition and phase boundaries, calculated isotherms (equation of state, EOS), transient clusters and their lifetime and charge state, the angular distribution function of H3 clusters, mixing of H and H2 liquid, thermal fluctuation analysis, isotope effect, finite size effects, and the assessment of proton selfdiffusivity and viscosity.

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“…These techniques are very challenging for low-atomic-number elements such as hydrogen [15]. Fortunately, optical phonon modes disappear, appear, or experience sudden shifts in frequency when the crystal structure changes.…”

Section: Introductionmentioning

confidence: 99%

Nature of the metallization transition in solid hydrogen

2017

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We present an accurate study of the static-nucleus electronic energy band gap of solid molecular hydrogen at high pressure. The excitonic and quasiparticle gaps of the C2/c, P c, P bcn, and P 6 3 /m structures at pressures of 250, 300, and 350 GPa are calculated using the fixed-node diffusion quantum Monte Carlo (DMC) method. The difference between the mean-field and many-body band gaps at the same density is found to be almost independent of system size and can therefore be applied as a scissor correction to the mean-field gap of an infinite system to obtain an estimate of the many-body gap in the thermodynamic limit. By comparing our static-nucleus DMC energy gaps with available experimental results, we demonstrate the important role played by nuclear quantum effects in the electronic structure of solid hydrogen.

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New Phases and Dissociation-Recombination of Hydrogen Deuteride to 3.4 Mbar

Abstract: We present infrared absorption studies of solid hydrogen deuteride to pressures as high as 3.4 megabar in a diamond anvil cell and temperatures in the range 5 to 295 K. Above 198 GPa the sample transforms to a mixture of ! HD , ! !

Cited by 25 publications

References 42 publications

Understanding high pressure molecular hydrogen with a hierarchical machine-learned potential

Understanding high pressure molecular hydrogen with a hierarchical machine-learned potential

Thermodynamic anomalies and three distinct liquid-liquid transitions in warm dense liquid hydrogen

Nature of the metallization transition in solid hydrogen

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